Source-sink process of microplastics in watershed-estuary-offshore system

Microplastics have been found everywhere and caused most significant pollution on earth, especially to the marine environment. However, microplastic pollution of marine environment is rarely studied based on the watershed-estuary-offshore system. In this study, a technical analysis framework of source-sink process of microplastics has been proposed based on watershed-estuary-offshore system. The impacts of human activities and hydrologic conditions on the microplastic distribution patterns in the sediments of Laizhou Bay were investigated. It is found that the river input from watershed to estuary is the main pathway for the microplastics in coastal areas to enter the sea. Population clusters, such as cities, towns and rural areas are increasingly important microplastic emission hotspots in the Laizhou Bay. Social and economic activities, productions and lifestyles in the watershed area have significant impacts on the distribution of microplastics, and the urbanization intensifies the process. A microplastic unit source-concentration response matrix model is established to simulate the transport of microplastics in the Laizhou Bay, which further confirm that river inputs are an important source of microplastics in the watershed-estuary-offshore system. It can also be concluded that the concentration of microplastics in river sediment is mainly affected by the natural conditions of the upstream watershed, the scale of human activities and the level of urbanization.